Short Circuit Brake for wind turbine generator.

[PierreNunes]

Hello, team.

I bought a permanent magnet wind turbine (10kW; 1200 V; 8.5 amps), the blades are 2.75 meters long and the RPM for maximum power is 290.

After doing some research, I discovered the possibility of installing a short-circuit brake, which would be simple and cheap, but I believe that simply short-circuiting the phases during a storm could also be catastrophic for the generator.

Could you please advise me on this subject? Should I use resistors or batteries in the braking circuit?

Best wishes
Pierre

 

[waross]

My experience with short circuit braking is to stop charging when the batteries are fully charged.
Short circuiting stops the rotation.
Your challenge will be to determining when to apply the brake and how to avoid brake cycling during lulls in a storm.
When the phases are shorted there is almost no voltage and little current.
Multiple brake cycling during a storm may do damage.

 

[PierreNunes]

Hi waross, thanks for sharing your experience, I am going to connect it to the power grid, so I won't use batteries.

I am planning to use a three phase contactor with jumpers shorting the phases, which the coil will be activated by high temperature or excessive power or anything that occurs with strong winds. The blades are strong enough to survive due a hard brake but I guess if I install on each phase big resistors which will demands a lot of current it will slow down the rotor softer, If that is possible, would you know how to calculate this resistors?

 

[waross]

If that is possible, would you know how to calculate this resistors?

The lower resistance the better.
Zero Ohms may be optimum.
But, beware of repeated braking.
Your greatest stress, both electrical and mechanical will be braking to a stop from speed.
There will be little stress while actually stopped.

 

[jpts]

Couple of things come to mind:

1) You should check is the generator designed to handle the short-circuit without demagnetization of the magnets. Some companies cut costs and use cheap magnets which are not designed to withstand the demagnetizing field due to short-circuit. If this happens, your generator is basically dead. Or at least you would need to replace the rotor

2): If the torque due to stormy wind exceeds the short-circuit torque, generator starts to spin and you will quite fast burn the stator. Short-circuit torque is high at first, but if this peak short-circuit torque is exceeded (due to wind), then the braking short-circuit torque drops to much lower value, and there might be nothing to stop it from spinning until it fails